Patent Document 1 below describes such a piston casting method, in which a pair of main molds forming an outer peripheral face of the piston and a pair of side cores forming the pair of cutout recess parts are prepared, the main molds and the cores are set so as to form a cavity corresponding to the piston, the cavity is charged with molten metal, and after the piston within the cavity has solidified, the pair of side cores are made to descend along a linear path in a direction in which they are moved away from a piston center face in going downward, thus carrying out mold release from the cutout recess parts.